1. Field of the Invention
The present invention relates to a molded motor provided with: a stator; a rotor rotatably disposed inside the stator; and a molded main body composed of resin which covers the stator.
2. Description of the Related Art
FIG. 3 is a cross-section of a conventional molded motor, and this molded motor is provided with: a stator 1; a rotor 2 rotatably disposed inside the stator 1; bearings 3 disposed at both ends of the rotor 2 to support the rotor 2 so that it can rotate freely; and a molded main body 4 composed of resin which covers the stator 1.
The stator 1 is provided with: a stator core 6 laminated from a plurality of layers of thin cold-rolled steel plate 5, which is a magnetic plate (the stator core 6 shown in FIG. 3 is a cross-section along line A--A of the stator core 6 in FIG. 4); stator coils 8 mounted on the tooth portions 22 of the stator core 6; a first guide 9 and second guide 10 which fit into the stator core 6 from the top and bottom respectively to insulate between the stator coils 8 and the stator core 6; and a terminal 11 fixed by heat crimping to the second guide 10 and connected to the stator coils 8.
The cold-rolled steel plate 5 has a plurality of tooth portions 22 extending radially inward which are formed equidistantly around it.
The rotor 2 is provided with: a shaft 12 supported at both ends by the bearings 3 so that it can rotate freely; and magnets 13 fixed to the shaft 12 with adhesive, arranged with alternating north-seeking (N) poles and south-seeking (S) poles.
The molded main body 4 has: a connector portion 40; flange portions 15 integrated with bushes 14 into which bolts (not shown) are inserted; and a receiving portion 17 which receives an annulus 16, which is an inserted body.
The molded motor of the above construction is connected by means of bolts inserted into the bushes 14 to a throttle valve device, which regulates the amount of air delivered to an internal combustion engine.
The throttle valve device is provided with: an annulus 16 which is inserted into the receiving portion 17 of the molded main body 4 and which has an internal gear 18 on its inner wall; a sun gear 19 connected to the shaft 12; a planetary gear (not shown) which engages with the sun gear 19 and the internal gear 18; and a shaft (not shown) which passes through the center of the planetary gear.
In the molded motor of the above construction, the molded main body 4 is formed integrally with the stator 1 by insertion molding, in which resin is injected into a metal mold in which the stator 1 and a bush 20 have been placed, then the bearing 3, which is secured to the shaft 12, is inserted into the bush 20, and the stator 1 and rotor 2 are integrated.
In the molded motor of the above construction, rotating magnetic fields of north-seeking (N) poles and south-seeking (S) poles are generated in the stator core 6 by passing an electric current through the stator coils 8, and the magnets 13 and the shaft 12 secured to the magnets 13 follow this rotating magnetic field and rotate.
The sun gear 19 of the throttle valve device rotates with the rotation of the shaft 12. The planetary gear, which is engaged with the sun gear 19 and the internal gear 18 of the annulus 16, rotates and revolves around the sun gear 19. With the rotation of the planetary gear, a shaft and a gear (not shown) rotate and the throttle valve (not shown) rotates. The amount of air delivered to the internal combustion engine varies in response to the rotational angle of this throttle valve.
In the conventional molded motor, the annulus 16, which is an inserted body, is inserted into the receiving portion 17 formed in the molded main body 4, but because the molded main body 4 is formed from resin, the engaging portion 17a of the receiving portion 17 may not be formed in a true circle of the required dimensions due to variations in the thermal contraction of different portions of the molded main body 4 during natural cooling, etc., and the axial center of the shaft 12 of the mold motor and the axial center of the annulus 16 of the throttle valve device may not be aligned, and thus; it suffers from the following problems:
a) the boss portion 21 of the annulus 16 cannot be inserted into the engaging portion 17a of the molded main body 4, and so product yield is poor; and PA1 b) the gears of the throttle valve device do not engage each other smoothly, and so undesired noise is generated and the gears wear down in a short time.